Supplemental signalling system for special railway track equipment



G. D. BOGEL ETAL SUPPLEMENTAL. SIGNALLING SYSTEM FOR SPECIAL RAILWAY TRACK EQUIPMENT Feb. 26, 1963 Filed W5. 12. 1957 5 Sheets-Sheet 1 WEST g ow

Inventors GhDnBo gel w. .B. Edi/Jon By, /M, @www&J/)IQZZM fl+tornegs United States Patent 3,079,496 SUPPLEMENTAL SIGNALLING SYSTEM FOR SPECIAL RAILWAY TRACK EQUIPMENT Graham D. Bogel, 3110 E. La Salle, Colorado Springs,

(1010., and Willie B. Wilson, 5907 Lawrence St., Am-

arillo, Tex.

Filed Dec. 12, 1957, Ser. No. 702,320 14 Claims. (Cl. 246167) This invention is an improvement on the system described in Grosjean Patent No. 2,630,524, issued March 3, 1953, and relates to a supplemental signalling system for use in conjunction with existing block signal systems of railway for protecting special track equipment that is used along the railway and that is characterized by the fact that it does not interfere with the control of train traffic since it does not activate the block signal system.

Such special equipment may include the usual railway motor cars or similar types of railway vehicles or it may include special portable indicating equipment that is carried by maintenance gangs working along the track.

, The principal object of the invention is to provide a system for actuating an indicator located on a motor car or other special track equipment to warn of the approach of a train in ample time to permit such equipment to be removed from the track.

Another object is to provide such a system without interfen'ng with the normal operation of the block signal system that governs train traffic.

Still another object is to provide a system of this type that requires but a minimum'amount of auxiliary equipment. j

Other objects include the provision of a more sensitive and reliable indicating system that embodies frequencysensitive apparatus for detecting the presence and/or direction of approach of trains.

According to the invention an indicator is provided for each motor car or other equipment that is to be warned of the approach of a train. The indicator includestwo frequency-selective channels, one to indicate the approach of a train from one direction and the other to indicate the approachof a train from the opposite direction. Apparatus is provided for applying two alternating-current signals to the tracks for actuating the indicator. One of the signals is of the frequency towhich one of the indicator channels is sensitive and the other signal is of the frequency to which the other indicator channel is sensitive. 5

This system is employed in conjunction with a railway-signalling system which employs the usual direct-current track circuits for governing train traffic, and the alternating-current signals will not affect the track relays of the track circuits. Similarly, the special equipment which is to be warned according to the invention will not shunt the track circuits but responds only to alternating currents of the predetermined frequencies. The apparatus for supplying the alternating-current signals which control the indicator is arranged to respond to the approach of a train from either direction and temporarily remove the particular signal that corresponds to the approach of a train from such direction. The sensing of the approach of a train may either be carried out by line circuits under the control of the existing track relays or by the use of additional alternating-current signals, each of unique frequency characteristic, that are applied directly to the sections of track adjacent the particular section under surveillance.

Other objects and advantages will become apparent during the course of the following description.

In the accompanying drawings forming a part of this specification and in which like numerals are employed to designate like parts throughout the same,

"ice

FIGS. 1 and 2, when placed side-by-side with FIG. 1 at the left, comprise a diagrammatic illustration of a stretch of railway track having the usual track circuits for controlling train traffic and including the supplemental signalling system of the invention;

FIG. 3 is a diagrammatic view of a modification of the supplemental signalling system of the invention and corresponds generally to the group of track sections shown in FIG. 1; and

FIG. 4 is a diagrammatic view of the indicator apparatus and circuitry, including the connection to the motor car axle.

In general, in the drawings the relay contacts are aligned with the coil of their controlling relay, though in certain instances it has appeared more appropriate to separate the contact from its controlling coil; and to facilitate checking the circuit operation, the relays and contacts associated therewith are designated by corresponding reference characters.

Referring now to the drawings and particularly to FIGS. 1 and 2, placed side-by-side with FIG. l at the left,

. the main track is divided into a plurality of successive the coils is negligible.

track sections designated 1T to 111, with the track sections having the usual insulated joints I between their adjacent ends. The track circuits are conventional and include at one end thereof a track relay TR energized through the rails thereof by a track battery TB at the other end thereof. The batteries TB are shown connected to the track rails through an inductive reactor I to prevent alternating current signals from being'shunted through the battery. This reactor I preferably has a low D.C. resistance and an inductive reactance of several ohms at the lowest frequency used in the system. The track relays require no modification since they are not responsive to'alternating current signals and since the impedance'of their coils is so high that the loss of alternating-current energy through The above modifications apply both to steady D.C. track circuits and to coded D.C. track circuits.

In certain instances the track circuits are additionally modified by bridging non-shorting, high-capacity capacitors C around certain of the insulated joints I between sections. These capacitors couple alternating-current signals between adjacent track sections and, in effect, link a number of track sections'together to' form a more extensive protected section. In this way a single installation of warning apparatus may serve -a protected section that includes a number of the usual track sections. The protected sections are isolated one from another by virtue of the fact that the insulated joints therebetween are not pro vided with by-pass capacitors. Thus, for example, the joint between track sections ST and 4T is not bridged by a capacitor and defines the opposite limits of adjacent protected sections. The same is true of the joint between track sections 7T and ST. This particular arrangement of the track sections into the more extensive protected sections by means of the by-pass capacitors does not in any way interfere with the normal operation of the track circuits.

As indicated at the joint between track sections 6T and 7T, the protected sections may be extended to any desired range by bridging the insulated joint by a transistor amplifier 17 having its input and output coupled between the adjacent track circuits respectively. Such amplifier arrangements may also be employed where excessive loss of alternating-current signal energy is experienced due to poor ballast conditions.

In the system of the present invention, each protected section is supplied with two alternating-current signals of distinctive frequency characteristic. Preferably, the signals are of fixed but different frequencies. It may be seen that a typical protected section includes track sections 4T throughTI, and there is applied to this typical protected section an alternating-current signal of a first fixed frequency through an input supply arrangement EF1 and an alternating-current signal of a second fixed frequency through an input supply arrangement WFI To eliminate the necessity of bridging the joint between sections T and (ST, this supply equipment is positioned at this joint with two separate sets of leads being extended from each of the supplies to the track circuits. In the case of the EF1 supply, one set of leads feeds the track circuit for section 5T through the (1) contacts of the corresponding approach circuit relay EAR and the other set of leads feeds the track circuit for section 6T through the (2) contacts of the corresponding'approach circuit relay 10EAR. Similarly, for the WFl'supply, one set of leads feeds the track circuit for section 5T through the 1 conta cts) of the approach circuit relay 10WAR and the other set of leads feeds the track circuit for section 6T through the (2) contacts ofthe approach circuit relay 10WAR.

Each protected section preferably has two approach circuits associated with it, with one approach circuit extending in the east direction and the other extending in the west direction suitable distances to allow ample time for clearing the protected section upon the approach of a train. The use of two separate approach sections permits of directional indication, and this is desirable. In the arrangement of FIGS. 1 and 2, line circuits 10B and 10W comprise the east approach circuit and west approach circuit, respectively, for the protected section that includes track sections 4T, 5T, 6T and 7T. Thus, the east approach circuit 10E includes an approach relay IOEAR in series-connection with the -1) contacts of track relays 6TR through 11TR. Similarly the west approach circuit includes approach relay 10WAR in series-connection with the (1) contacts of track relays lTR through 5TR.

The protected section which includes track sections 8T, 9T, 10T, and 11T has an east approach circuit 20E that includes an approach relay 20EAR in series-connection with the (2) contacts of track relays llTR and additional track relays (not shown) that would belocated to the'right of llTR, and a west approach circuit 20W that includes an approach relay 20WAR in series-connection with the (2) contacts of track relays STR through 10TR. v

Finally, the protected section which includes track sections 1T, 2T and 3T has an east approach circuit 3013 that includes an approach relay '30EAR in seriesconnection with the (3) contacts of track relays 2TR through STR and a west approach circuit 30W that into prevent attenuation of the voltage of the desired alternating-current signals until such desired voltage becomes high enough to energize the appropriate indicator relay properly. The amplifiers in the illustrated arrangement are provided with automatic gain control and negative feed-back to stabilize the gain over a wide range of temperature and battery voltage. In this connection, a bias battery B1 is provided to delay the action of the automatic gain control system until the actuating voltage is sufiicient to operate the relay.

Details of the design and operation of an example of the receiver amplifier circuit are as follows: The input circuit of the receiver amplifier is connected to the track rails through slip rings SR on the wheels of the vehicle. Capacitor C1 prevents shunting of the DC. track circuit and permits passage of alternating currents only to the input circuit of the receiver. 7 1

Semiconductor diodes D1 and D2 are connected t shunt the input circuit. The resistance of these diodes, being high at very low voltage, do not shunt to any great extent when the input voltage is low, but as the input voltage is raised above the minimum required toencrgize the indicator, the effective resistance of diodes D1 and D2 becomes lower and shunts a larger proportion of the input voltage. This increases the voltagedrop across series resistor R1 such that the diodes D1 and D2 function to limit the alternating-current voltage applied to input circuits ET and WT. Since it would require a much higher voltage of some other frequency than the prescribed frequency to energize the relays ER and WR, this limiting action prevents false cnergization of these relays by any other alternating frequency that might be present on the track rails. 1

Tuned circuit ET is resonant to frequency EF1 and passes this frequency to transistor EQI and tends to reject other frequencies. Transistor EQl amplifies the EF1 energy and passes it to transistor EQ2 through the resonant circuit EIl, which serves a double purpose of matching the output impedance of EQl to the input impedence of EQ2 and adding more selectivity forfrequency EF1. Transistor EQ2 further amplifies the EF1 frequency and transmits it on to EQ3 through a resonant circuit ET2, which performs the same function as previously explained for ETl. EQ3 further amplifies theEF'l cludes an approach relay 30WAR and the (3) con- 7 tacts of track relays lTR and additional track relays (not shown) that'would be located to the left of '1TR.

The indicator employed in the present system, as shown in FIG. 4, is equipped with a dual-channel receiver 40 and separate indicating relays ER and WR for each channel. Thus the east channel is shown at the top of FIG. 4, and it includes a three-stage transistor amplifier which energizes a sensitive D.C. relay ER through a bridge-type rectifier ERX. Similarly, the west channel, which is shown at the bottom of FIG. 4, includes a threestage transistor amplifier which energizes indicating relay WR through a rectifier-type bridge WRX.

The input to the dual-channelreceiver from the track rials is connected to the amplifiers through resonant-circuit arrangements ET'and WT which are tuned, respectively, to the alternating-current signals EF1 and WFI: This input circuit for the amplifiers includes diodes D1 and D2, which, in conjunction with resistor R1, act as an input limiter and prevent the input voltage from becoming high enough'to cause false operation by stray alterna-ting-current signals of a frequency other than the frequency-selected for use in the supplemental signalling system. *Ihe initialresistan'ceof the diodes is sufficient frequency and transmits it to bridge rectifier ERX through resonant circuit E13. Transistor EQ3 is a POWCILOUt' put type of transistor which is capable of suflicient output to energize relay ER through rectifier ERX, which recti fies the EF1 output of EQ3 to produce direct current to energize relay ER.

As a further safeguard against false energization of relay ER by any frequency other than EF1, the automatic gain control circuit consisting of resistor ER3, capacitor ECl, resistor ER2, diode EDI and battery EBI is provided. The alternating-current voltage developed across ER3 in the emitter circuit of transistor EQ2 is rectified by the semi-conductor diode EDl to produce a negative DC. voltage which is applied through the battery EB1 to the emitter of transistor EQl to provide automatic gain control. This negative DC. voltage reduces the gain of EQl and prevents its output voltage from exceeding a safe level. The battery BB1 is selected and connected with proper polarity and voltage to prevent automatic gain control action until the voltage of EF1 is sufiicient to energize relay ER. Relay ER, energized, lights a green light--de-energized, lights a red light. The transisto ramplifier at the bottom of FIG. 4 is identical to the one at the top except that its input and coupling circuits are resonant to frequency WFl and performs the same function with WF1 as described above for EF1.

As mentioned previously, the supplemental signalling system of the invention is intended for use on the usual railway motor cars, though it may, as well, be employed in connection with special portable indicating equipment that is carried by the maintenance gangs and connected 5. by suitable flexible leads from a wayside location to the track rail. For purposes of disclosure, only the use in connection with motor cars need by described.

In the case of a motor car, the indicating apparatus of FIG. 4 is mounted on the vehicle in front of the operator for ready visibility. As shown in FIG. 4, a typical motor car to which the invention is applicable may include a wheel arrangement wherein the wheels W, each of which is in electrical contact with the rail on which it rides, are insulated by means of an insulated joint I] provided in the axle connecting the wheels. Thus, the motor car does not operate to shunt the track rails. Alternating-current signals in the track rails are connected to the input circuit for the receiver 40 through the usual slip rings SR.

The indicating apparatus is arranged to provide a red light and/or green light indication for each channel. It will be remembered that in the absence of train trafiic, the alternating-current signals are continuously applied to the track sections under surveillance so that any car along these sections will continuously pick up these signals. Thus, the indicating relays ER and WR of FIG. 4 are normally energized, and their contacts normally connect the green light portion of the warning circuit to indicate that there are no trains within a predetermined distance of the car.

Upon the approach of a train to the sections under surveillance, the alternating-current signal in the track corresponding to the direction of approach of the train will be terminated, as will be described hereinafter, and the corresponding indicating relay becomes de-energized, dropping its contact to interrupt the green light portion of the circuit and establish the red light portion. Thus, the operator on the vehicle is informed of the presence and direction of an approaching train. If desired, an audible signal may also be actuated to warn of the ap proach of a train.

To illustrate the operation of the track circuit portion of the supplemental signalling system, reference is again made to FIGS. 1 and 2. It will be assumed that the equipment which is to be warned of the approach of a train is located somewhere within the protected section that includes track sections 4T through 7T, and it will be assumed that a train is approaching from the east and is just entering track section 11T. As the train enters section 11T, its wheels shunt the direction-currenttrack circuit and cause track relay 11TR to become de-energized, thereby opening series-contact 11 TR1 of the east approach circuit B and de-energizing the east approach relay 10EAR. This drops contacts 10EAR-1 and NEAR-2 and removes the alternating-current signal EF1 from the protected track section 4T through 7T. Since relay ER is energized and lights the green light only when frequency EF1 is being received, relay ER is now de-energized, extinguishing the green light for the east channel and lighting the red one to indicate a train east of the motor car. As described, the light indicator of the east channel changes from green to red and remains red until the motor car is removed from the track.

Instead of employing separate line circuits for the approach circuits, the invention contemplates an alternative arrangement wherein the rails themselves may be employed to complete the approach circuits. Such an arrangement is shown in FIG. 3, wherein a protected section again extends from track sections 4T to 7T, inclusive. It will be noted in this arrangement that the joint between track sections ST and 6T is provided with bypass capacitors C. The general arrangement of the direct-current track circuits may be identical to the arrangement shown in FIGS. 1 and 2, though, for simplicity, the track circuits are not shown. Once again the alternating-current signals for controlling the indicating apparatus are designated EF1 and W1 and with respect to the protected section 4T through 7T, it may be seen that the EF1 signals are applied at the east end while the WFl signals are applied at the west end.

Since the approach circuit is provided by the rails in this case, two additional alternating-current signals, EFZ and WFZ, preferably of fixed but difierent frequencies, are applied directly to the rails of each protected section. Thus, signal EF2 is applied at the east end of protected section 4T to 7T and is detected by a tuned receiver amplifier 40E for controlling relay 30EAR, which contrials the application of EF1 signals to the protected section that includes track sections 3T and 2T. Thus the rails of protected section 4T to 7T, in conjunction with the EF2 supply at the east end thereof, form the approach circuit for the protected section that includes track sections 2T and 3T. Similarly the rails of track sections ST and the sections to the east thereof, which include a source (not shown) of EFZ signals, in conjunction with the tuned receiver-amplifier 41B and relay IOEAR, form the east approach circuit for the protected section that comprises track sections 4T through 7T. The west approach circuit for protected section 4T through 7T comprises a source (not shown) of WFZ signals and the rails of the protected section of which track sections 2T and 3T are a part, in conjunction with the tuned receiveramplifier 42W and relay 10WAR. Finally, the west approach circuit for the protected section of which section 8T is a part includes the rails of protected section 4T and 7T, the tuned receiver-amplifier 43W, and relay ZOWAR. The east approach circuit for the protected section of which -8T is apart is not shown nor is the west approach circuit for the protected section of which track sections 2T and ST are a part.

The operation-of the supplemental signalling system of FIG. 3 is essentially the same as that for the system of FIGS. 1 and 2. For purposes of illustration, the operation will be described in connection with a; train approaching from the east, and it will be assumed that the train has just entered upon the section of track that constitutes a part of the east approach circuit for protected section 4T through 7T. As soon as the train enters this approach circuit, it shunts the alternating-current energy supplied to this east approach circuit at its east end (not shown) from a source of EFZ energy. Therefore, the approach of the train causes relay IOEAR to become de-energized, thereby removing the EF1 signals from protected sections 4T to 7T. The indicator on-a vehicle within this protected section will then respond in the manner previously described.

As the train proceeds in its approach from-the east and enters section 7T, it will shunt the east approach section for the protected section of which track sections 2T and ST are a part and thus will de-energize relay EGEAR, thereby causing EF1 signals to be removed from this protected section.

It will thus be seen that the objects of this invention have been accomplished in that the system provides a directional indication of the approach of a train to a motor car on a protectedsection of track or to other types of special equipment electrically connected across the rails of a protected section of track. In addition, it provides such indications without interfering with the normal operation of the block signals system, and it requires but a minimum amount of auxiliary equipment. As disclosed, the system is preferably frequency-sensitive so that it will not respond to spurious signals that may exist, and it includes amplification facilities so that the signals applied to the rails and transmitted therethrough need only be of sufficient strength as to permit their indication. Such an arrangement otters obvious advantages over systems wherein the signals in the rail must be of sufiicient strength to actuate relays directly.

The system of the invention has been described in its most basic form, and numerous refinements will occur to those skilled in this art; for example, traflic stick relays can be used to supply alternating-current signals to the 7 track behind a train after the train has passed the point where the alternating-current signals are coupled to the track.

It should be understood that the description of the preferred form of the invention is for the purpose of complying with Section 112, Title 35, of the US. Code and that the claims should be construed as. broadly as prior art will permit. a

We claim: a

1. In combination with a stretch of railway track divided into a plurality of protected sections each having a track relay which is normally energized by current supplied to the rails of its section and which releases due to the shunting effect of the wheels and axles when a train occupies its section, said stretch being provided with a railway-signalling system controlled by said track relays for governing the movement of trains through said stretch from one end to the other end thereof, a supplemental signal system for warning equipment in said stretch that is connected across the rails thereof and that is not adapted to shunt said track relays, said supplemental signal system comprising indication means connected across the rails and selectively responsive to current in the track rails of a character different from that normally supplied to said track relay and to which current of distinctive character the track relays are nonresponsive, means for applying said current of distinctive character to the rails of at least one of said sections, means for applying another current to the rails of sections of track adjacent said one section,- said last-mentioned current being applied to said adjacent sections at the ends thereof remotefro-rn said one section and being different in character from that supplied to the track relays of {said adjacent sections and being such that the track relays are non-responsive thereto, and means adjacentthe other ends of said adjacent'sections responsive to said last-mentioned current thereat and connected to the first-named means for applying current to maintain the application of current of distinctive character to said one section only when said adjacent sections are not occupied.

2. In combination with a protected section of railway track provided with a track relay which is normally energized by current supplied to the track rails and which releases due to :the shunting effect of the wheels and axles when a train occupies said section, said relay controlling a railway-signalling system for governing the movement of trains through said section, a supplemental signalling systeni for warning equipment in said section that is connected across the rails thereof and that is not adapted to shunt said track relay, said supplemental signalling system comprising indicating means on said equipment connected across the rails of said section and selectively responsive in the absence of either one current or the other current therein, said one current and said other current each being of distinctive character to which said relay is non-responsive and each being different from the current normally supplied to said track rails, supply means connected across the rails of said one section for simultaneously supplying said one and said other currents thereto, with said one and said other current corresponding respectively to first and second track positions spaced in opposite directions from said section and means responsive to the presence of a train at one of said positions and connected for selectively controlling said supply means to terminate the supply to said section of only the one of said currents corresponding to the position of the train and thereby cause a selective response of said indicating means.

3. A supplemental signalling system for use with a protected section of railway track provided with a track relay which is normally energized by direct current supplied to the track rails and which releases due to the shunting effect of the wheels and axles when a train occupies said section; said system warning special equipment that is electrically connected across the rails of said section but is not adapted to shunt the direct current from said track relay and comprising indication means on said equipment and selectively responsive in the absence of either one of two alternating currentsignals to be provided in the track rails to correspond, respectively, to first and second track positions spaced in opposite directions from said section, with each signal being of a unique frequency characteristic and being of such nature that said relay is non-responsive thereto, supply means connected across the rails of said section and normally supplying said alternating current signals thereto simultaneously, and means responsive to the presence of a train at one of said positions and connected for selectively controlling said supply means to terminate the supply to said sectionof the one of said signals corresponding to the position of the train and thereby cause a selective response of said indicating means.

4. In combination with a stretch of railway track divided into a plurality of protected sections each having a track relay which is normally energized by current supplied to the rails of its section and which releases due to the shunting eifect of the wheels and axles when a train occupies its section, said stretch being provided with a railway-signalling system controlled by said track relays for governing the movement of trains through said stretch from one end to the other end thereof, a supplemental signal system for warning equipment in said stretch that is connected across the rails thereof and that is not adapted to shunt said track relays, said system comprising indication means selectively responsive to current in the track rails of a character dilferentfrom that normally supplied to said track relay and to which current of distinctive character the track relays are non-responsive,- means for applying said current of distinctive character to the rails of at least one of said sections, means for supplying another current to sections of track adjacent said one section, said last-mentioned current being applied to said adjacent sectionsat the ends thereof remote from said one section and being different in character from that supplied to thetrack relays of said adjacent sections and being such that the track relays are non-responsive thereto, and means adjacent the other ends of said adjacent sections responsive to said last-mentioned current thereat and connected to the first-named means for applying current to terminate the application of said current of distinctive character to said one section when said adjacent section is occupied. I

5. A supplemental signalling system for a stretch of railway track along which special equipment, as well as trains, is operated, said special equipment being connected across the track rails for electrical response only to alternating currents therein, the rails of said stretch being divided into a plurality of successive protectedtrack sections each provided with a track circuit comprising a track relay and a source of direct current connected across the rails thereof such that said circuits are shunted by trains but not by said special equipment:

said supplemental signalling system comprising indication means on said equipment and selectively responsive to two alternating current signals in the track rails, with each signal being of unique frequency character;

istic and being of such nature that said relays are non responsive thereto; supply means normally supplying said alternating current signals simultaneously to the rails of each of said sections; means responsive to the presence in said stretch of a train and connected for selectively" controlling said supply means to terminate the supply to the protected track section of the one of said signals,

corresponding to the direction in which the trainis spaced from the protected section, saidrneansincluding second supply meansfor simultaneously applying tofther rails of each of said sections two additional alternating current signals each of individually unique frequency characteristic suchthat the rails of any intermediate section of said stretch normally carry said first-mentioned two alternating current signals and the sections adjoining such intermediate section normally carry said two additional alternating current signals, first means for each intermediate section selectively responsive to one of said two additional alternating current signals in one of the sections adjoining such intermediate section for maintaining, only during the period when said one adjoining section is not occupied, the supply to said intermediate section of the one of said two first-mentioned signals that corresponds to the spacing direction of a train relative to said intermediate section, and second means for each intermediate section selectively responsive to the other of said two additional alternating signals in the other section adjoining said intermediate section for maintaining, only during the period when said other adjoining section is not occupied, the supply to said intermediate section of the other of said two first-mentioned signals.

6. A supplemental signalling system for use with a protected section of railway track provided with a track relay which is normally energized by direct current sup-' plied to the track rails and which releases due to the shunting effect of the wheels and axles when a train occupies said section; said supplemental signalling system warning special equipment that is electrically connected across the rails of said section but is not adapted to shunt the direct current from said track relay and comprising frequency-sensitive indication means on said equipment and selectively responsive only in the absence of'either one of two alternating current signals to be provided in the track rails to correspond, respectively, to'first and second track positions spaced in opposite directions from said section, with each signal being of a unique fixed frequency and being of such nature that said relay is non-responsive thereto, supply means connected across the rails of said section and normally supplying said alternating current signals thereto simultaneously, and means responsive to the presence of a train at one of said positions and connected for selectively controlling said supply means to terminate the supply to said section of only the one of said signals corresponding to the position of the train and thereby cause a selective response of said'indicating means.

7. A supplementalsignalling system for a stretch of railway track along which special equipment, as well as trains, is' operated, said special equipment being connected across the track rails for electrical response only to alternating currents therein, the railsof said stretch being divided into a plurality of successive protected track sections each provided with a track circuit comprising a track relay and a source of direct current connected across the rails thereof such that said circuits are shunted by trains but not by said special equipment; said supplemental signalling system warning said special equipment and comprising frequency-sensitive indication means on said equipment and selectively responsive only in the absence of either one of two alternating current signals to be provided in the track rails to correspond, respectively, to first and second track positions spaced in opposite directions from the particular protected section to which the special equipment is connected, with each signal being of a unique fixed frequency and being of such nature that said relays are non-responsive thereto, supply means normally supplying said alternating current signals simultaneously to the rails of each of said sections, and means responsive to the presence of a train at one of said positions and connected for selectively controlling said supply means to terminate the supply to said last-mentioned section of only the one of said signals corresponding to the position of the train. 8. A supplemental signalling system for a stretch of railway track along which special equipment, as well as 10' trains, is operated, said special equipment being connected across the track rails for electrical response only to alternating currents therein, the rails of said stretch being divided into a plurality of successive protected track sections each provided with a track circuit comprising a track relay and a source of direct current connected across the rails thereof such that said circuits are shunted by trains but not by said special equipment: said supplemental signalling system comprising frequency-sensitive indication means on said equipment and selectively responsive only in the absence of either one of two alternating-current signals in the track rails, with each signal being of unique fixed frequency and being of such nature that said relays are non-responsive thereto; supply means normally supplying said alternating-current signals simultaneously to the rails of each of said sections; means responsive to the presence in said stretch of a train and connected for selectively controlling said supply means to terminate the supply to the protected track section of the one of said signals corresponding to the direction in which the train is spaced from the protected section, said means including second supply means for simultaneously applying to the rails of each of said sections two additional alternating-current signals each of a unique fixed frequency such that the rails of any intermediate section of said stretch normally carry said first-mentioned two alternating-current signals and the sections adjoining such intermediate section normally carry said two additional alternating-current signals, first means for each intermediate section tuned to and responsive to current of the unique frequency of one of said two additional alternating-current signals in one of the sections adjoining such intermediate section and connected to the first-mentioned supply means for maintaining, only during the period when said one adjoining section is not occupied, the supply to said intermediate section of the one of said two firstmentioned signals that corresponds to the spacing direction of a train relative to said intermediate section, and second means for each intermediate section tuned toand responsive to current of the unique frequency of the other of said two additional alternating signals in the other section adjoining said intermediate section and con nected to the first-mentioned supply means for maintaining, only during the period when said other adjoining section is not occupied, the supply to saidintermediate section of the other of said two first-mentioned signals;

9. A supplemental signalling system for a stretch of railway track along which special equipment, as well as,

trains, is operated, said special equipment being connected across the track rails for electrical response only to alternating currents therein, the rails of said stretch being divided into a plurality of successive major track sections with insulated joints defining the limits of said major sections and'with each major section being divided into a plurality of successive minor track sections, with insulated joints defining the limits of said minor sections, each minor section being provided with a track circuit comprising a track relay and a source of direct current connected across the rails thereof such that said circuits are shunted by trains but not by said special equipment, electrical means conductive only to alternating-current signals bridged across the insulated joints between the minor track sections of each major section; indication means on said equipment and selectively responsive in the absence of either one of two alternating-current signals in the track rails, with each signal being of unique frequency characteristic and being of such nature that said relays are non-responsive thereto; separate supply means for each major section normally supplying said alternating current-signals simultaneously to the rails of each of said sections, separate control means for each supply means responsive to the presence in said stretch of a train and connected for selectively controlling the corresponding supply means to terminate the supply to the major track sections of the one of said signals corresponding to the direction of spacing of the train therefrom, said control means including second supply means for each major section simultaneously applying to the rails thereof two additional alternating-current signals each of individually unique frequency characteristic such that the rails of any intermediate major section of said stretch normally carry said first-mentioned two alternating-current signals and the major sections adjoining such intermediate section normally carry said two additional alternating-current signals, first means for each intermediate section selectively responsive to one of said two additional alternating-current signals in one of the sections adjoining such intermediate section and connected to the first-mentioned supply means for such section for maintaining, only during the period when said one adjoining section is not occupied, the supply to said intermediate section of the one of said two first-mentioned signals that corresponds to the direction in which said one adjoining section is spaced rom said intermediate section, and second means for each intermediate section selectively responsive to the other of said two additional alternating signals in the other section adjoining said intermediate section and connected to the first-mentioned supply means for such section formaintaining, only during the period when said other adjoining section is not occupied, the supply to said intermediate section of the other of said two first-mentioned signals.

'10. In combination with a stretch of railway track divided into a plurality of protected sections each having a track relay which is normally energized by current applied to the rails of its section and which releases due to the shunting effect of the wheels and axles when a train occupies its section, said stretch being provided with a railway-signalling system controlled by said track relays for governing the movement of trains through said stretch from one end to the other end thereof, a supplemental signalling'system for warning equipment in said stretch that is connected across the rails thereof and that is not adapted to shunt said track relays, said supplemental signalling system comprising supply means connected across the-rails of at least one of said sections for individually and simultaneously supplying first and second currents thereto corresponding, respectively, to first'and second positions in said stretch spaced in opposite directions from said one section, said first current and said second current each being of individually distinctive character to which said relays are non-responsive and each being different from the current normally supplied to said track relays, means responsive to the presence of a train at onecof said positions and connected for controlling said supply means to terminate the supply to said one section of the current corresponding to the position of the train, and indicating means connected across the rails of said section and selectively responsive to the absence of either one of said first and second currents for indicating the presence of the train at a position corresponding to the absent current.

11. A supplemental signalling system for a stretch of railway track along which special equipment, as well as trains, is operated, said special equipment being connected across the track rails for electrical response only to alternating currents therein, the rails of said stretch being divided into a plurality of successive major track sections with insulated joints defining the limits of said major sections and with each major section being divided into a plurality of successive minor track sections, with insulated joints defining the limits of said minor sections, each minor section being provided with a track circuit comprising a track relay and a source of direct current connected across the rails thereof such that said circuits are shunted by trains but not by said special equipment, electrical means conductive only to alternating-current signals bridged across the insulated joints between the minor track sections of each major section; said supplemental signalling system comprising separate supply means connected across the rails of each major track section with each supply means individually and simultaneously supplying first and second alternating-current signals to its major section, said first and second alternating-current signals corresponding, respectively, to first and second track positions spaced in opposite directions from such major section, each alternating-current signal being of unique frequency characteristic and being of such nature that said relays are non-responsive thereto, separate means for each major track section responsive to the presence of a train at one of said positions and connected for controlling the supply means for such major track section to terminate the supply to said one section of the alternating-current signal corresponding to the position of the train, and indicating means connected across the rails of one of said sections and selectively responsive to the absence of either one of said first and second alternatingcurrent signals. 7

12. In combination with a stretch of railway track divided into a plurality of protected sections each having a track relay which is normally energized by current supplied to the rails oi its section and which releases due to the shunting effect of the wheels and axles when a train occupies its section, said stretch being provided with a railway-signalling system controlled by said track relays for governing the movement of trains through said stretch.

from one end to the other end thereof, a supplemental signalling system for warning equipment in said stretch that is connected across the rails thereof and that is not adapted to shunt said track relays, said supplemental signalling system comprising supply means connected across the rails of one of said sections for individually and simultaneously supplying first and second currents thereto corresponding, respectively, to first and second positions in said stretch spaced in opposite directions from said section, said first current and said second current each being of individually distinctive character to which said relays are non-responsive and each being diflferent from the current normally supplied to said track relays, means responsive to the presence of a train at one of said positions and connected for controlling said supply means to terminate the supply to said one section of the current corresponding to the position of the train, and indicatingmeans connected across the rails of said one section for selectively indicating the absence of one of said currents. 13. In combination with a stretch of railway track divided into a plurality of protected sections each having a track relay which is normally energized by current supplied to the rails of its section and which releases due to the shunting effect of the wheels and axles when a train occupies its sections, said stretch being provided with a railway-signalling system controlled by said track relays for governing the movement of trains through said stretch from one end to the other end thereof, a supplemental signalling system for warning equipment insaid stretch that is connected across the rails thereof and that is not adapted to shunt said track relays, said supplemental signalling system comprising supply means connected across the rails of at least one of said sections for individually and simultaneously supplying first and second currents thereto corresponding, respectively, to first and second positions spaced in opposite directions from said section, said first current and said second current each being of individually distinctive character to which said relays are non-responsive and each being diiferent from the current normally supplied to said track relays, means responsive to the presence of a train at one of said positions and connected for controlling said supply means to terminate the supply to said one section of the current corresponding to the position of the train, and indicating means connected across the rails of said section and having means responsive to the presence of both said first and second currents for indicating that said section is clear of trains and means selectively responsive to the absence of either one of said first and second currents for indicating the 13 presence of the train at the position corresponding to the absent current.

14. A supplemental signalling system for a stretch of railway track along which special equipment, as well as trains, is operated, said special equipment being connected across the track rails for electrical response only to alternating currents therein, the rails of said stretch being divided into a plurality of successive major protected rack sections with insulated joints defining the limits of said major sections and with each major section being divided into a plurality of successive minor track sections, with insulated joints defining the limits of said minor sections, each minor section being provided with a track circuit comprising a track relay and a source of direct current connected across the rails thereof such that said circuits are shunted by trains but not by said special equipment, electrical means conductive only to alternating-current signals bridged across the insulated joints between the minor track sections of each major section; said system comprising indication means on said equipment and selectively responsive in the absence of either one of two alternating-current signals in the track rails, with each signal being of unique frequency characteristic and being of such nature that said relays are non-responsive thereto; seperate supply means for each major track section normally supplying said alternating-current signals simultaneously to the rails of each such major track section; and separate means for each major track section responsive to the presence in a major track section adjacent one end of said last-mentioned major track section of a train and connected for selectively controlling said supply means to terminate the supply to said last-mentioned section of the one of said signals corresponding to the position of the train and thereby cause a selective response of said indicating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,786,815 Aspinwall Dec. 30, 1930 1,791,168 Sasnett Feb. 3, 1931 1,816,628 Williams et a1 July 28, 193] 2,611,075 Marlowe Sept. 16, 1952 2,617,922 Thompson Nov. 11, 1952 2,630,524 Grosjean Mar. 3, 1953 2,794,117 Rees et al. May 28, 1957 2,816,218 Rees et al. Dec. 10, 1957 2,822,463 Thompson Feb. 4, 1958 

1. IN COMBINATION WITH A STRETCH OF RAILWAY TRACK DIVIDED INTO A PLURALITY OF PROTECTED SECTIONS EACH HAVING A TRACK RELAY WHICH IS NORMALLY ENERGIZED BY CURRENT SUPPLIED TO THE RAILS OF ITS SECTION AND WHICH RELEASES DUE TO THE SHUNTING EFFECT OF THE WHEELS AND AXLES WHEN A TRAIN OCCUPIES ITS SECTION, SAID STRETCH BEING PROVIDED WITH A RAILWAY-SIGNALLING SYSTEM CONTROLLED BY SAID TRACK RELAYS FOR GOVERNING THE MOVEMENT OF TRAINS THROUGH SAID STRETCH FROM ONE END TO THE OTHER END THEREOF, A SUPPLEMENTAL SIGNAL SYSTEM FOR WARNING EQUIPMENT IN SAID STRETCH THAT IS CONNECTED ACROSS THE RAILS THEREOF AND THAT IS NOT ADAPTED TO SHUNT SAID TRACK RELAYS, SAID SUPPLEMENTAL SIGNAL SYSTEM COMPRISING INDICATION MEANS CONNECTED ACROSS THE RAILS AND SELECTIVELY RESPONSIVE TO CURRENT IN THE TRACK RAILS OF A CHARACTER DIFFERENT FROM THAT NORMALLY SUPPLIED TO SAID TRACK RELAY AND TO WHICH CURRENT OF DISTINCTIVE CHARACTER THE TRACK RELAYS ARE NONRESPONSIVE, MEANS FOR APPLYING SAID CURRENT OF DISTINCTIVE CHARACTER TO THE RAILS OF AT LEAST ONE OF SAID SECTIONS, MEANS FOR APPLYING ANOTHER CURRENT TO THE RAILS OF SECTIONS OF TRACK ADJACENT SAID ONE SECTION, SAID LAST-MENTIONED CURRENT BEING APPLIED TO SAID ADJACENT SECTIONS AT THE ENDS THEREOF REMOTE FROM SAID ONE SECTION AND BEING DIFFERENT IN CHARACTER FROM THAT SUPPLIED TO THE TRACK RELAYS OF SAID ADJACENT SECTIONS AND BEING SUCH THAT THE TRACK RELAYS ARE NON-RESPONSIVE THERETO, AND MEANS ADJACENT THE OTHER ENDS OF SAID ADJACENT SECTIONS RESPONSIVE TO SAID LAST-MENTIONED CURRENT THEREAT AND CONNECTED TO THE FIRST-NAMED MEANS FOR APPLYING CURRENT TO MAINTAIN THE APPLICATION OF CURRENT OF DISTINCTIVE CHARACTER TO SAID ONE SECTION ONLY WHEN SAID ADJACENT SECTIONS ARE NOT OCCUPIED. 